A few months back, in the fall of 2019, a handful of current and former staffers from the Earth Resources Observation and Science (EROS) Center met at a gathering spot in Sioux Falls to remember an old friend.
Though the world may stare blankly when it hears the name Advanced Very High Resolution Radiometer (AVHRR), long-timers at the Center know better. More than anyone else, they understand how this imager aboard a series of National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites sharpened the waning remote-sensing focus of the EROS Science Branch in the later 1980s and launched it into national and international remote-sensing importance.
Because it did, and because the last in a long line of NOAA AVHRR imagers is no longer transmitting useful data to measure important vegetation greenness across the planet, it seemed a good time to get together for one last auld lang syne.
“If you’ve been at EROS a long time, and you know that people have done a lot of work to keep something going that has been very important to us here at the Center, then it seems worth noting, worth recognizing,” said USGS Research Geographer Jesslyn Brown, who was at the gathering. “For a lot of us, AVHRR was a big deal.”
A big deal? In the mid-1980s, EROS Science was at a crossroads. The government’s decision to commercialize the Landsat system and turn it over to EOSAT virtually priced Landsat images out of Center scientists’ ability to use them for scientific applications. The longstanding practice in the branch of buying an image and doing a small study somewhere in the country for a stakeholder was coming to an end.
Those projects weren’t having the impact they once did anyway, said retired EROS Chief Scientist Tom Loveland. Other organizations had figured out they could invest in their own capabilities to do those studies themselves, he added, “so, we really were at a critical point that where EROS science goes, and for that matter where EROS goes, was really a big issue.”
USGS EROS Geographer Gray Tappan recalled it as a time of great fears—unfounded or not—that the Center might actually have to close. To ward off that possibility, EROS Director Al Watkins gave Don Moore a mandate in 1986 to develop an international program at EROS while also expanding the Science Branch’s research and applications work, Tappan said.
“Don already had experience doing international projects with USAID (U.S. Agency for International Development) in West Africa and the Middle East, and he loved that stuff,” Tappan said. “So, Al gave him the green light to go ahead and develop this international program ... to help us diversify and put us on the world map and keep the Center open. It was perfect.”
Moore immediately set off for Washington, D.C., to walk the halls at USAID headquarters, knock on doors, and ask what the agency had going on in Africa. What were the environmental issues they were dealing with? What was the drought situation? How can we help?
NASA had started doing greenness mapping at a coarse scale in 1982. Moore knew that, so he and Loveland went back to Washington, D.C., again with a pledge that EROS could composite daily images from the NOAA AVHRR data and create detailed country-by-country greenness maps every two weeks for such things as studying drought. USAID liked what it heard and agreed to fund it.
So it was that Center scientists and geographers walked boldly into the international remote-sensing world. One of their first steps was out onto the fringes of Africa’s Sahara Desert to help address a major plague of desert locusts—the biblical kind that devour whole crops at a time, Tappan said.
Using AVHRR greenness maps shipped from EROS, he could show officials with Crop Protection Service agencies in Africa where the landscape was greening up because of rainfall, and where the moist soil was most likely acting as excellent incubation for locust eggs.
“It was one of the most perfect applications of remote sensing we have ever done in this science branch,” Tappan recalled. “Trying to get out with airplanes and Land Rovers to monitor vast areas where conditions might be good for locusts was expensive. But we could direct them with these greenness maps, and they’d go out to specific areas and more easily find them. They could then follow up with treatments, with aerial spraying.”
Other uses for the EROS-produced greenness maps followed. Loveland said they conducted several studies across Africa to look at establishing drought monitoring centers using AVHRR. That resulted in a partnership with the AGRHYMET Center in Niamey, Niger, that led to drought monitoring and other food security activities in the Sahel area of West Africa.
Computers and plotters were shipped to Niamey, Loveland said. The USGS had an antenna installed on the roof at AGRHYMET, “and we created an operational West African vegetation-condition monitoring program that took over what we were doing here at EROS,” he said.
Similar conversations went on with East Africa as well. And after a discussion with the northern half of Africa, officials with the Tunisian government decided to implement greenness mapping and do the work themselves, Loveland said.
Back in those days, a USAID project called Famine Early Warning Systems (FEWS)—which later became the FEWS Network—was using AVHRR data provided by NASA to monitor drought conditions and thus potential food insecurity in Africa and elsewhere. When the USGS brought 1-kilometer AVHRR data to AGRHYMET as part of a separate USAID-funded activity, FEWS eventually moved to using that USGS product as well.
“All that then led into the early Nineties, to a recognition that issues like drought, food insecurity, and other global change need global imagery,” Loveland said. “So, through the International Geosphere-Biosphere Programme, a global AVHRR initiative was started, and we ran it here at EROS. And that led to our national and global land cover work here.”
Back home, a second significant impact of AVHRR on the future of EROS had played out in 1987 when NOAA agreed to shift $600,000 from its budget to the USGS to pay for a 3-meter Viasat antenna to go on the Center’s roof to acquire AVHRR data. For the first time, it showed EROS’ capability to do more than simply archive remotely sensed data and act as a lab to produce satellite imagery. With AVHRR, EROS could now successfully manage a ground station, a realization that helped pave the way for a Landsat ground station at the Center in the future.
Brown started using AVHRR in 1989, working with Kevin Gallo at the Center making graphics with Global Vegetation Index data. In 1988, a great drought across the Northern Plains helped prove the ability of initial AVHRR products to monitor vegetation health here in the United States. A year later, EROS started producing wall-to-wall vegetation greenness images for the conterminous U.S., Brown said.
“These products coming out in near real time were great for operational uses,” she said. “And we couldn’t have done it without the dish on our roof providing data every day.”
In that sense, AVHRR with its daily acquisitions and its biweekly composites showed the first potential of looking at landscapes and land cover change across time, and in near real time. In many ways, it showed the potential of using remote sensing in a time domain, spurring the evolution of such ideas as data cubes and inspiring the possibility of future endeavors like the USGS’ Land Change Monitoring, Assessment, and Projection (LCMAP) initiative.
AVHRR enabled the compilation of Normalized Difference Vegetation Index (NDVI) images at EROS to measure vegetation conditions across the U.S.—allowing for not only the estimation of the location and amount of green vegetation, but also the comparison of that information to the relative norm from the previous week, year, or 30-year average.
Those NDVI compilations were useful in measuring fire fuel loads and dangers, particularly in the western states. And Brown made AVHRR the centerpiece of her work with drought monitoring through two important drought indices—the Vegetation Drought Response Index (VegDRI) and Quick Drought Response Index (QuickDRI).
“My career has been certainly supported by these data,” she said. “It really supported a lot of interesting research. For scientists, we’re always poking around and wanting to find a reason for something, and AVHRR provided that.”
Or at least it did. Knowing that the AVHRR imager on the NOAA-19 satellite would be the last, Brown and others began transitioning to NASA’s Moderate Resolution Imaging Spectrometer (MODIS) and eMODIS data long ago with its equally good temporal resolution and higher resolution data. Now with MODIS sensors aboard NASA’s Terra and Aqua satellites aging as well, the next generation sensor—the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership and NOAA-20 weathers—is the future of greenness mapping.
Against that reality—and with the last NOAA satellite carrying the AVHRR imager now having slipped too far out of its necessary orbit to provide scientifically sound data anymore—it seemed to some at least a good time to reflect on an old war horse and its impact on EROS.
“The lessons learned with AVHRR and refined during the MODIS era are now the foundation for how people are using Landsat,” Loveland said. “So, in many ways, AVHRR has had a massive impact on the world, and where we are at EROS are today.”